Prostate cancer cells rely on androgen receptor
(AR) signalling for growth and survival, and this dependence is exploited for
treatment of metastatic prostate cancer by inhibition or reduction of available
androgen in the patient. This treatment ultimately fails, and we propose that
more effective inhibition of AR signalling through combinatorial strategies may
improve patient outcomes. Histone deacetylase inhibitors (HDACIs) and AR antagonists
are two distinct classes of clinical agents that are known to modulate levels
and/or activity of the AR. We have shown that the combination of vorinostat, a
HDACI, and bicalutamide, an AR antagonist, significantly enhances death of
prostate cancer cells. In this study, we investigated whether this combination
relies solely on enhanced androgen blockade for its apoptotic effect, or if a
unique mechanism is responsible. LNCaP human prostate cancer cells were treated
with bicalutamide and vorinostat, alone or in combination, and RNA was analysed
on Affymetrix Human Genechip Gene 1.0 ST Arrays. Analysis of the resulting gene
profiles showed that a substantial number of the genes modulated by the
combination were androgen regulated, however, qRT-PCR validation of a subset of
these genes showed that the combination did not further alter their expression
over bicalutamide alone. This indicated that the combination mechanism of
action may not be completely explained by enhanced androgen blockade. Further
pathway analysis implicated NFKBIA
loss, leading to deregulation of NF-κB
and p53 signalling, as a potential mechanism. Specific knockdown of NFKBIA resulted in significant cell
death similar in magnitude to that observed with combination treatment,
implicating NFKBIA as a key regulator
of prostate cancer cell survival. Taken together, our data suggest that while the
combination of vorinostat and bicalutamide blocks androgen signalling in
prostate cancer cells, it also causes deregulation of NF-κB and p53 signalling
which may mediate cell death induced by this treatment.